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Old 12-02-2011, 22:08   #16
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It really is a design issue. CE seems to be pretty darn fast with raster charts, and the price to pay is rendering quality.

PolarView tries to get better rendering quality, so raster chart handling in PolarView is comparatively slow.

There has to be a trade-off there, especially in quilting products.

Here is the same area in PolarView, just for comparison.
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Old 13-02-2011, 04:59   #17
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Jiffylube (may I call you Jif): You are almost correct: If the places moved or chart items were missing, the "real" chart would be the test, but clearly that is impossible when two programs render the same electronic image - I think I got that right with Dan's help.

I did compare the chartlet I chose with a chart book I own of the area. The Cap'n is a better rendering. More important, I compared the renderings with "ground truth". The smaller items are more accurately represented.

Finally, I compared the two chartlets with my view of what a chart should be - this is what started the comparison in the first place. CE falls short by rendering fine lines fuzzy, blurring fine features and while not exactly making it unsafe, or even harder, to navigate, CE reduces the experience my making me work harder or sometimes guess what the original raster chart showed.

I prefer raster charts for near shore fine detail navigation. Until CE is improved, I guess I'll use another rendering tool.
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Old 13-02-2011, 08:32   #18
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It occurred to me that CE might be trying to conserve memory, which is always in short supply when handling large images. Typically, a raster is read once and stored (the reference image). It is then rescaled and displayed as the user selects different locations and scales. By storing the reference image at somewhat reduced resolution, you can save memory but rendering will suffer when zoomed way in. CE tries to reduce memory use by reading only the needed horizontal slices of KAP files. Readers familiar with the KAP file format will understand why this can work pretty well.

Some BSB charts have more resolution than is needed for a decent display at the original scale. Pixelization tends to occur only when the image is displayed overscale. The crisp, clear details are an illusion. (the illusion can be even worse with vector charts)

I know that Rosepoint takes a hard line on overscale use, so they may have decided that using more memory to allow crisp overscale display was a bad idea. I'm speculating about this of course. The problem with this approach is that you need to get the numbers right. If reasonable scales look fuzzy, customers will (and have, it seems) notice. On the other hand, crisp overscale display is a waste and possibly even unsafe, in spite of the overscale warnings.

It is possible that they have the right idea and just need to tune it slightly. It is also possible that they need to revisit some old design decisions to reflect an era where several gigabytes of RAM is common on even cheap laptops. My guess is that the whole raster thing is just not at the top of Rosepoint's priority list.

Although these comments might sound a bit negative, I really like CE and plan to keep using it.

Charlie
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Old 13-02-2011, 09:38   #19
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Charlie,

When the Cap'n was new, memory was a major constraint. They provided a "crappy" and a "superior" setting on resolution. This worked ok on my early Pentium processor and early version of windows.

Memory constraints are different than they were at one time, as you correctly noted. Best I can tell, on the Cap'n, low and high resolution are both high resolution.

Neat displays, user assistance, location of the nearest bar are all good additional tools in a navigation program - they led me to recommend CE to several people when I delivered their boats.

But, the best possible chart rendering is the minimum acceptable chart rending for me since I frequently enter constrained spaces in my shallow draft sailboat. I know it isn't critical for everyone, but if CE made design decisions that result in less than the best possible chart, that is unacceptable for me. I understand vector charts have a more complete picture under some situations, but I remain a raster user and want the higher quality rendering I've come to expect from a quality chart program.

I'm confident they will change their design decision once the differences in rendering are clear to the designers.
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Old 13-02-2011, 19:15   #20
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The difference in the displays has nothing to do with memory or lack of quality or any of the other things I've seen mentioned. The difference has to do with the scaling that was performed and the antialiasing done in Coastal Explorer to make their charts better.

Coastal Explorer will quilt all charts in an area together and then display them at any scale. So quilting together a 1:40,000, 1:80:000, and 1:15,000 chart and then rotating them to undo NOAA's skew and displaying them at a chosen scale of 1:45,000 will result in some pretty complex image processing. If you don't do it with antialiasing, the resulting display will look pretty disgusting and appear to have broken pixels.

PolarView's display is antialiased too but I think that screen shot was done at a scale closer to the original of the chart. A proper comparison should have all displayed scales identical.

A couple of questions about the Cap'n version you're using:

- Does it quilt the charts together into a single seamless chart?

- Can you select any scale desired or does it only display the chart in multiples of the chart's native scale (1:40,000 chart would only be displayed as 1:20,000, 1:80,000, etc)?

- Can you make a screen shot of what the Cap'n chart shown previously looks like when it's rotated by 30 degrees?


There is a lot at work with raster graphics to balance the output between having displays that look good and ones that accurately represent the original scanned chart. In almost all cases, a quilted chart with antialiasing like Coastal Explorer and PolarView provide have much better results than the "nearest-neighbor" type of scaling done in the screen shot of the Cap'n shown in this thread.

Someone asked about the trial version of PolarView that I don't think was answered. The trial version renders charts with the full fidelity of the real version. The only real difference between the trial version and the real version is that the trial times out. Entering an activation code into the trial version makes it a real version.

ActiveCaptain is either a dealer or has worked closely with all of the various chart software developers. In addition, I spent a couple of afternoons in Dennis Mill's dining room in Bangor Maine where The Cap'n was written back almost 20 years ago. I used my first copy around 1995. I'm not very familiar with the current version of the Cap'n which appears to be having it's share of difficulties today after a variety of companies have bought and sold the the product leaving it now in another transitionary period.
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Old 14-02-2011, 04:52   #21
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Jeffery, Thank you for your comments - some quoted below.

"The difference has to do with the scaling that was performed and the antialiasing done in Coastal Explorer to make their charts better."

>I tried to use the same scale for the Active Captain (AC) and Cap'n. The second screen image published was done with only one file made available to the Cap'n.>

"PolarView's display is antialiased too but I think that screen shot was done at a scale closer to the original of the chart. A proper comparison should have all displayed scales identical."

<Polar View was not loaded on the computer used for the screen shots.>

"A couple of questions about the Cap'n version you're using:

- Does it quilt the charts together into a single seamless chart?"

> No. Cap'n was run with a data set containing only a single file for the test. The version of Cap'n tested does not support quilting.?

"- Can you select any scale desired or does it only display the chart in multiples of the chart's native scale (1:40,000 chart would only be displayed as 1:20,000, 1:80,000, etc)?"

<Both CE and the Cap'n have tools that permit arbitrary scales. CE uses a slide bar in the tool bar, Cap'n uses in and out zoom buttons. I tried to select the same sale and tested to see if larger or smaller scales would improve the result.>

"- Can you make a screen shot of what the Cap'n chart shown previously looks like when it's rotated by 30 degrees?"

<No, I run North up.>

" In almost all cases, a quilted chart with antialiasing like Coastal Explorer and PolarView provide have much better results than the "nearest-neighbor" type of scaling done in the screen shot of the Cap'n shown in this thread."

<Maybe we should share an understanding of "Better". Better, to me, is the closest possible representation of the underlying paper Government chart. Eliminating small canals or features is not better.">

I used my first copy around 1995. "

<I, also, began using Cap'n in the mid 90's. My current, licensed, version is from about 1998. Unfortunately, it is no longer supported, even for a fee I'm willing to pay, and no longer supports tides.">

<While I have some understand of the difficulties involved in rendering the best possible image for the intended purpose in all conditions, I continue to believe the CE image of the areas I sail and have tested is inferior to the same image rendered by the much, much older Cap'n software.

<This is about getting there and home safely. Clearly, no one can say that a more accurate chart image will prevent an accident, but it might. The standard of excellence of an electronic chart rendering package is not really debatable, it should render a chart at least as well as a new, Government issued, chart of the same area. My 20+ year old version of the Cap'n does this and the software I replace it with will also - not a very high bar to jump. >

Thank you, again, for your comments. Makes us all think clearer. /Stu
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Old 14-02-2011, 07:48   #22
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CE

Here is aside by side of CE and Polar View



Same chart from same file on hard disk
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Old 14-02-2011, 08:13   #23
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Quote:
Originally Posted by r.fairman View Post
Same chart from same file on hard disk
Notice the honking big warning message in the middle of the Coastal Explorer image!

One of the things I like about raster charts is that when they are zoomed in past the resolution of the data, the image generally becomes more difficult to see. That gives you an immediate indication that you can't rely on every pixel for navigation. That isn't the case in vector/ENC/S-57 charts. You can zoom infinitely in and the lines and text are just as clear as possible and you're left with little visual cues about whether the data is really valid.

That said, it's pretty obvious that PolarView is doing a pretty nice job of image processing to make the display look good. For what it's worth, our newsletter last week extolled the virtues of PolarView and recommended it to our users. The new release is pretty nice and by the way, has ActiveCaptain support for marinas, anchorages, local knowledge, and hazard markers.
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Old 14-02-2011, 15:53   #24
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When it comes to raster charts, it's almost like the old saying of "Cheap, Fast, High Quality - pick any two".

Only for raster charts it's "Quilted, Fast, High Quality Rendering - pick any two"
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Old 14-02-2011, 15:57   #25
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Only for raster charts it's "Quilted, Fast, High Quality Rendering - pick any two"
That's quite true! I like that.
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Old 14-02-2011, 16:14   #26
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It is hard to compare the renderings above with the two I published - they are of different places and the CE rendering is overscale - all bets are off when you do something the vendor warned against. How about a side by side with the same area of the keys?

/Stu
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